Many liquid processing mechanisms cause a liquid to foam. In many cases, such as beer making, foaming may occur during various steps of making and cooling wort, as well as fermentation. Foam may be an undesirable byproduct of a processing step or may be a desirable outcome where the foam may separate and transport undesirable components away from a desired component.
Foam may contain a large amount of gas and, over time, may collapse into a relatively small amount of liquid.